Question 1

An amplifier enzyme catalyzes the synthesis of a second messenger.

Accepted Answer

Amplifier enzymes, such as adenylyl cyclase or guanylyl cyclase, catalyze the synthesis of second messengers like cyclic AMP (cAMP) or cyclic GMP (cGMP) from ATP or GTP, respectively, amplifying the signal within the cell.

Question 2

Steroid hormones are derived from the hormone testosterone.

Accepted Answer

Steroid hormones are derived from cholesterol, not directly from the hormone testosterone. Testosterone itself is a type of steroid hormone.

Question 3

Steroid hormones are produced within cells and stored in vesicles until they are released.

Accepted Answer

Steroid hormones are synthesized from cholesterol in the smooth endoplasmic reticulum and mitochondria and are not stored in vesicles; they diffuse across cell membranes as they are produced due to their lipophilic nature.

Question 4

The location of the receptor depends on whether the messenger is lipophilic or lipophobic.

Accepted Answer

Lipophilic messengers typically pass through the cell membrane and bind to intracellular receptors, while lipophobic messengers cannot pass through the lipid bilayer and bind to receptors on the cell surface.

Question 5

If calcium channels open in the plasma membrane, calcium ions enter the cell.

Accepted Answer

Calcium channels in the plasma membrane allow for the selective passage of calcium ions into the cell, following their concentration gradient.

Question 6

Generally, the nervous system is a more rapid means of communication than the endocrine system.

Accepted Answer

The nervous system communicates through electrical impulses and neurotransmitters, allowing for quick responses, while the endocrine system relies on hormones transported through the bloodstream, which takes longer.

Question 7

A single cell can have receptors for different messengers.

Accepted Answer

A single cell can have receptors for various types of messengers, including hormones, neurotransmitters, and cytokines, allowing it to respond to different signals from the body or environment.

Question 8

In its active form, a G protein has a GDP bound to its alpha unit.

Accepted Answer

In its active form, a G protein has GTP bound to its alpha unit, not GDP. GDP is bound to the alpha unit in its inactive form.

Question 9

Tyrosine is one of four amino acids that function directly as chemical messengers.

Accepted Answer

Tyrosine is an amino acid involved in the synthesis of proteins and the production of neurotransmitters, but it is not classified as one of the primary chemical messengers itself. Chemical messengers typically refer to molecules like hormones or neurotransmitters directly involved in signaling, such as epinephrine or norepinephrine, which can be synthesized from tyrosine.

Question 10

Tyrosine kinases are enzymes that add a phosphate group to tyrosine residues on other proteins, changing the conformation of those proteins.

Accepted Answer

Tyrosine kinases are indeed enzymes that catalyze the phosphorylation of tyrosine residues in proteins, which can alter the protein's function and conformation.

Question 11

Eicosanoids are released immediately upon synthesis.

Accepted Answer

Eicosanoids are synthesized on demand from arachidonic acid present in cell membranes and are released immediately upon synthesis to perform their biological functions, as they are not stored in cells.

Question 12

The target cell of a neurotransmitter is the postsynaptic cell.

Accepted Answer

The target cell of a neurotransmitter is indeed the postsynaptic cell, as neurotransmitters are released from the presynaptic cell and bind to receptors on the postsynaptic cell to transmit signals across the synaptic gap.

Question 13

Most receptors are relatively non -specific for the ligand that will bind to them.

Accepted Answer

Receptors are typically highly specific for their ligands, meaning they are designed to bind very specific molecules or a very narrow range of molecules with high affinity. This specificity is crucial for the precise control of biological processes.

Question 14

Thyroid hormones alter the transcription of mRNA in the target cell.

Accepted Answer

Thyroid hormones enter target cells and bind to intracellular receptors, which then directly interact with DNA to modify the transcription of mRNA, affecting protein synthesis and altering cell function.

Question 15

All catecholamine -secreting cells synthesize dopamine.

Accepted Answer

All catecholamine-secreting cells synthesize dopamine because it is a precursor in the biosynthetic pathway for norepinephrine and epinephrine, which are also catecholamines.

Question 16

Enkephalin is an opiate produced in the body. When enkephalin binds to opioid receptors, it produces analgesia (a lack of pain sensation). Morphine can also bind to opioid receptors and produce analgesia. Morphine is an opiate antagonist.

Accepted Answer

Morphine is an opiate agonist, not an antagonist, because it activates opioid receptors to produce analgesia, similar to enkephalins.

Question 17

The higher concentration of messenger, the greater the response in the target cell.

Accepted Answer

The concentration of a messenger (such as a hormone or neurotransmitter) typically correlates with the magnitude of response in the target cell. Higher concentrations often lead to a greater response due to more receptors being activated.

Question 18

Endocrine glands secrete neurohormones.

Accepted Answer

Endocrine glands secrete hormones directly into the bloodstream, not neurohormones, which are produced by neurosecretory cells.

Question 19

Receptors for lipophilic chemical messengers are only located on the surface of a cell's membrane.

Accepted Answer

Receptors for lipophilic (hydrophobic) chemical messengers are typically located inside the cell, either in the cytoplasm or the nucleus, because these messengers can easily cross the cell membrane.

Question 20

Lipophobic chemical messengers communicate a message to the target cell by binding to receptors on that cell's membrane.

Accepted Answer

Lipophobic (or hydrophilic) chemical messengers cannot easily cross the lipid bilayer of cell membranes, so they bind to receptors on the surface of the target cell to communicate their message.

Quiz 5: Chemical Messengers